Unit cells of a source cell portion with a MOSFET including a current sensor are disposed in a source pad. Unit cells of a current-sensor cell portion with a MOSFET including a current sensor are also disposed in a current sensor pad.
Each of the unit cells of the source cell portion includes: an n+ buffer layer of n-type; an n− layer of n-type formed on the n+ buffer layer, a junction field effect transistor (JFET) n+ layer of n-type formed in a surface layer of the n− layer (hereinafter may be referred to as a “JFET n+ layer”); a p-base layer of p-type formed in the surface layer of the n− layer; a p+ layer of p-type formed in a surface layer of the p-base layer; an n+ source layer of n-type formed to sandwich the p+ layer in the surface layer of the p-base layer; gate polysilicon functioning as a gate electrode and formed above the p-base layer to sandwich a gate oxide film; an interlayer insulation film formed to cover the gate polysilicon; an Ni—Si layer formed across a part of the n+ source layer and the p+ layer; a source electrode formed to cover the interlayer insulation film and the Ni—Si layer; and a drain electrode formed on the back side of the n+ buffer layer.
Each of the unit cells of the current-sensor cell portion includes: an n+ buffer layer of n-type; an n− layer of n-type; a JFET n+ layer of n-type; a p-base layer of p-type; a p+ layer of p-type; an n+ source layer of n-type; gate polysilicon; an interlayer insulation film; an Ni—Si layer; a current-sensor electrode formed to cover the interlayer insulation film and the Ni—Si layer; and a drain electrode.
As described above, the unit cells in the source cell portion and the current-sensor cell portion basically have the same structure. The number of unit cells disposed in the current-sensor cell portion approximately ranges from 1/10000 to 1/5000 of the number of unit cells disposed in the source cell portion.
With the structure, the MOSFET including the current sensor allows a current that amounts to approximately 1/10000 to 1/5000 of the current flowing through the source to flow through the current sensor.
An intelligent power module (IPM) with a protection circuit uses a MOSFET chip including a current sensor (see, for example, Patent Document 1). When an overcurrent such as a short-circuit current flows between drain and source due to, for example, a load short-circuit in an inverter circuit, detecting a current flowing through the current sensor and feeding it back to the protection circuit can prevent an overcurrent failure in the IPM.